Abstract

We demonstrate a simple method to increase the optical density (OD) of cold atom clouds produced by a magneto-optical trap (MOT). A pair of rectangular anti-Helmholtz coils is used in the MOT to generate the magnetic field that produces the cigar-shaped atom cloud. With 7.2 × 10887Rb atoms in the cigar-type MOT, we achieve an OD of 32 as determined by the slow light measurement and this OD is large enough such that the atom cloud can almost contain the entire Gaussian light pulse. Compared to the conventional MOT under the same trapping conditions, the OD is increased by about 2.7 folds by this simple method. In anotherMOT setup of the cigar-shaped Cs atom cloud, we achieve an OD of 105 as determined by the absorption spectrum of the |6S1/2, F = 4〉→|6P3/2, F′ = 5〉 transition.

(a) Fluorescence images of the cigar-shaped atom cloud. The line of sight of the left image is along the z axis and that of the right image is along the x axis (the coordinate is illustrated in Fig. 1). (b) Fluorescence emitted by the trapped atoms versus time.

(a) The power of the optical pumping beam transmitted with (red line) and without (black line) the presence of the atoms versus time. (b) The difference of the black and red lines in (a). The area below the blue line indicates the number of the trapped atoms in the cigar-type MOT is 7.2 × 108.

The storage and retrieval of the probe pulse in (a) and the slow probe pulse under the constant presence of the coupling field in (b). Solid gray, black, and blue lines are the experimental data of the input and output probe pulses and the coupling field. The input probe pulse is plotted with the size reduced to one third. The data were measured with the cigar-shaped atom cloud of N = 7.2 × 108. Dashed gray and blue lines in (a) are the functions of the input probe pulse and the coupling field used in the calculation. Solid red lines in (a) and (b) are the best fits calculated at (α,Ωc, γ)=(32,0.330Γ,7.1 ×10−4Γ). Dotted blue lines in (b) have the same delay time as the solid red line, but are calculated at (38,0.365Γ,7.1 × 10-4Γ) and (26,0.295Γ,7.1 × 10−4Γ).

Transmission spectrum of the |6S1/2, F = 4〉→|6P3/2, F′ = 5〉 transition in lasercooled cigar-shaped Cs atom cloud. Black and red lines are the experimental data and the best fit. The fitting function is y = exp{-α/[1+4(x-x0)2]}, and α = 105 and x0=-0.35Γ for the best fit.